Whilst different people have different levels of tolerance for the amount of fat consumed, there is no denying it is a necessary part of the human diet – for nerve function, brain fuel, immune support, absorption of critical nutrients such as vitamins A, D, E and K, and it keeps us feeling satisfied.
We have heard for a long time that fats derived from animal sources are not good for you, and those derived from plants are.
Science sits on both sides of the fence when it comes to this broad sweeping argument. There are pros and cons for each. But perhaps we should be setting our focus on the degree of processing and how we consume the type of fat, rather than whether the fat is animal or plant sourced.
Sources of fats
Sources of animal fats include lard, tallow, butter, ghee, cream, eggs, fish and meat. Eating high amounts of meat, however, can mean consuming compounds that can cause oxidative stress to human cells – so if eating meat, eat your veg!
Plant-based fats are commonly sourced from avocado, coconut, olive, nuts and seeds. Oils tend to be from plant sources, including nut, seed, grain and fruit oils. Whilst we are told many oils are ‘vegetable’ oils, they actually fall into one of the former categories.
Some oils require minimal processing, such as coconut, olive and nut oils, which can be cold-pressed and bottled for our enjoyment. Wrenching oil from some seeds, however, can require a lot of work to get to the supermarket shelves.
It is these oils that have recently caused concern for their impact on our health, largely due to their fatty acid structure and stability.
Getting into the fatty science
Previously, we have discussed research on health impacts of saturated, monounsaturated and polyunsaturated fats.
Looking at fatty acid chemical structure, this can be affected by heat, light and exposure to oxygen, all at varying degrees depending on their stability. The impact of any of these elements – especially heat – causes bonds within the structure to break, creating oxidative products that fly around wildly damaging human cells.
Saturated fats have the most stable structure, and monounsaturated fats a little less so, and both seem to be good to cook with, and are also fine at room temperature.
Polyunsaturated fats are the least stable of the 3 main types of fatty acids, and also the source of omega-6 and omega-3 fatty acids.
A major consideration in choosing fats and oils to consume is the ratio of omega-3 to omega-6 fatty acid ratio. As discussed previously, we want this to be a 1:1-4 ratio. Both have benefits, such as cell membrane integrity, and providing anti-inflammatory and helpful pro-inflammatory activity.
But when out of balance, as is often the case in the 1:16 Western diet ratio, omega-6 fatty acids are too high. The omega-6 pro-inflammatory activity goes bonkers, too much for omega-3 to keep in check. This can contribute to the pathogenesis of cardiovascular disease, cancers, and autoimmune conditions.4
The science of fatty acids is all good and well – but let’s keep this simple. What should we be eating?
What to fat and what not to fat
What to fat?
Real, whole food fats and oils, as close to the their original form or as minimally processed as possible. This can include:
Monounsaturated fats. Reasonably stable at higher cooking temperatures, there is a plethora of science supporting health benefits for diets high in monounsaturated fats, particularly olive oil, especially around the cardiovascular system.
Omega-3 and Omega 6 (polyunsaturated) fats. These aren’t called essential fatty acids for nothing – we need them! Omega-3 fats can be sourced from oily fish, green leafy vegetables, and flax and chia seed, where as many oils are higher in omega-6. Polyunsaturated rich oils such as soy or canola can be less stable at higher temperatures3. Reserve for cold use, and choose those that are less processed and first cold pressed, like flaxseed or sunflower seed. As mentioned, omega-6 fatty acids are best had in ratio with its omega-3 cousin.
Whole food saturated fats and MCT. These are believed to hold their molecular structure at higher cooking temperatures. Coconut oil and butter contain higher amounts of saturated fat and medium-chain triglycerides (MCT) (a sub-classification of saturated fatty acids) than animal fats such as beef, chicken or fish. MCT are broken down earlier along the digestive tract, reducing the need for pancreatic enzymes to assist in the metabolism. This means it may be better tolerated for those who struggle to digest fats.
It is important to note that in a recent systematic review and meta-analysis, comparing consumption of saturated fats with trans fats on all cause mortality rates, cardiovascular disease and type 2 diabetes, saturated fat consumption fared far better.
Clearly high levels of industrialised trans fats cannot be great, but research is still in early days as to the long-term outcomes on high saturated fat intake. What may be more important is what we have been replacing the saturated fat with in the past, such as with sugars and refined foods. This does not seem to have done our health any favours.1;2
Generally, the closer to the original source, the better. Whole foods are ideal, such as avocado, olives, coconut, nuts, seeds, eggs, dairy, grass fed, free-range meats and poultry, and wild fish.
It comes down to the old mantra of just eating real, whole food.
What not to fat.
Highly processed seed oils. There is still much conjecture over the consumption of seed oils. Seed oils are largely comprised of polyunsaturated fatty acids that become unstable when exposed to high heat, light or oxygen. When unstable, they form free radicals, causing cellular damage, oxidative stress and inflammation.
If using these, choose expeller/unrefined/cold pressed version in dark, and preferably glass, bottles.
Margarine. Why even? Perhaps it served a purpose in early days of it introduction into the industrialised food world, but we have little need for it. Beside that, compared to butter it is highly processed – consider what it takes to extract oil from a seed and solidify it. What’s more, it is sometimes bleached to look similar to butter. Ick.
Trans-fats or partially hydrogenated fats. These are heavily manufactured or deep fried oils, often added as a cheap fat to various packaged goods, often from oils high in polyunsaturated fats.3 Having broken their molecular bonds during processing or through extreme heating, their cell damaging activity is high. Nasty.
Getting the best from your oil
Basically, you want to use oils that have the ability to remain stable at a molecular level, especially when cooked. Oils harder at room temperature are generally more stable at higher cooking temperatures. As light and oxygen can also impact the fatty structure stability, keep your oils stored in a cool, dark cupboard, preferably in a dark, glass bottle, and tightly sealed.
By Angela Johnson (BHSc Nut. Med)
- de Souza Russell J, Mente Andrew, Maroleanu Adriana, Cozma Adrian I, Ha Vanessa, Kishibe Teruko et al., 2015, ‘Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies’, British Medical Journal, no. 351, h3978.
- Micha, R, & Mozaffarian, D 2010, ‘Saturated fat and cardiometabolic risk factors, coronary heart disease, stroke, and diabetes: a fresh look at the evidence’, Lipids, vol. 45, no. 10, pp. 893-905.
- O’Keefe, S Gaskins-Wright, S Wiley, V CHEN, IC 2007, ‘Levels of trans geometrical isomers of essential fatty acids in some unhydrogenated U.S. vegetable oils’, Journal of Food Lipids, vol. 1, no. 3,
- Simopoulos, A 2002, ‘Dossier: Polyunsaturated fatty acids in biology and diseases: The importance of the ratio of omega-6/omega-3 essential fatty acids’, Biomedicine & Pharmacotherapy, vol. 56, pp. 365-379.